Preventing Transmission Mount Breakage

[greenjeep]

At the Rock Crawl last weekend my transmission mount tore apart which enabled my transmission to come slamming down onto my skid plate and punched a hole in my transmission pan. So I have been trying to come up with ideas on how to minimize the chance of breaking a transmission mount, as I've gone through several of them over the years.

I have MORE bomb proof motor mounts, and was running a stock rubber transmission mount. Here's what I was thinking, tell me what you think. Replace the rubber mount with a polyurethane mount to add rigidity, then take a couple eye bolts attached to ends of a length of chain and run that the chain over the top of the transmission and attached the eye bolts to the frame with the idea of minimizing the upward movement of the transmission.

I don't want to make my mounts so rigid that I began cracking my transmission housing, but I also don't want to keep breaking amounts. Also do you think a chain would eventually rub a hole in the transmission housing?

Any other suggestions, or words of advice. I can't imagine I'm the only one who's had this problem.

 

[Tacoma]

I think we talked about this for a second there-- All the mounts should be of the same material, to prevent any weak links...

Also, GM used struts tying the t-case to the block.. from the side of the case, up to one of the transmission bolts. Idea was to tie everything together and add rigidity...

I wouldn't use chains, they WILL wear a hole in the very thin, very soft top of a TH400. they're less than 1/4" thick.

 

[RockChucker]

what mount are you running? if i remember right your rig is a CJ on a TJ frame? are you running a TJ mount or a CJ one? what if you tried to adapt some sort of mount from a newer dmax or cummins? i would think that would hold up better seeing as they have enormous torque.

what t-case do you have? have you looked at making a mount that mounts to the rear of the tcase and ties in with your cross member? i have seen these done with atlases, would this be an appropriate/feasible solution for you? just some food for thought.

 

[greenjeep]

I think we talked about this for a second there-- All the mounts should be of the same material, to prevent any weak links...

Also, GM used struts tying the t-case to the block.. from the side of the case, up to one of the transmission bolts. Idea was to tie everything together and add rigidity...

I wouldn't use chains, they WILL wear a hole in the very thin, very soft top of a TH400. they're less than 1/4" thick.

I know that's what you said about running the same mounts, but it seems to me that the added rigidity of the MORE motor mounts would be more comparable to that of a polyurethane trans mount more so then a stock rubber trans mount.

So not a chain over the transmission, what about a ratchet strap, or is that to ghetto?

what mount are you running? if i remember right your rig is a CJ on a TJ frame? are you running a TJ mount or a CJ one? what if you tried to adapt some sort of mount from a newer dmax or cummins? i would think that would hold up better seeing as they have enormous torque.

what t-case do you have? have you looked at making a mount that mounts to the rear of the tcase and ties in with your cross member? i have seen these done with atlases, would this be an appropriate/feasible solution for you? just some food for thought.

I am running a CJ body on a TJ frame (good memory!), my TH400 and Dana 300 are from the CJ so I'm running a CJ style mount; the TJ mount is quite a bit different. I don't know about adapting a mount from a different vehicle, would they necessarily be stronger than a quality polyurethane one?

The problem with trying to run a mount off the end of my transfer case is that it sticks past my skid plate by about 4 inches, and is the only place I can put a jack when I have to take my skid plate off.

 

[skippy]

On mine after I did my 4 to 1 i was doing the same thing to transmission mounts the problem is the one mount driectly underneath the trans or t-case......So i built a new crossmember and just bolted a 3/8 plate to the bottom of the transmission tailhousing and then ran 2 poly bushings off each end of the plate so the bushings were out about 4 inches from the centerline of the trans and i havent had a problem since..........

 

[4554x4]

My solution

Dave, here is how I did my trans and motor mounts. I used suspension bushings and DOM. With much help from Casey Beach, I feel I will never have a problem.

I think you have exceded the limits of the factory design. You will have this problem multiple times with how/where you drive.

 

[greenjeep]

On mine after I did my 4 to 1 i was doing the same thing to transmission mounts the problem is the one mount driectly underneath the trans or t-case......So i built a new crossmember and just bolted a 3/8 plate to the bottom of the transmission tailhousing and then ran 2 poly bushings off each end of the plate so the bushings were out about 4 inches from the centerline of the trans and i havent had a problem since..........

I had been thinking about trying to redo a new design similar to the stock torque arm to help distribute load, yours sounds similar to what I was thinking.

Dave, here is how I did my trans and motor mounts. I used suspension bushings and DOM. With much help from Casey Beach, I feel I will never have a problem.

I think you have exceded the limits of the factory design. You will have a this problem multiple times with how/where you drive.

I think in the long run I'll need to go this route.

 

[thenag]

I'll throw out my thoughts on mounts, of course all my experience has do with a double t-case so hanging weight off the end of the tranny has been my problem.

In my old rig I had an 87 bronco with a 460, np435 and a np203/205 doubler.

I had stock 460 engine mounts which were pretty stout, and stock transmission mount which was crap, then a really stable mount on the back of the 205. After every trail run I had to tighten the bolts on the 203/205. My theory is that the motor was pretty tight and the 205 was really really tight but everything in the middle slopped around and worked the bolts loose.

the xj I just build up is a 4.0L with a ax-15 and a np231/d300. I am using the stock engine and transmission mounts and added a really small rubber mount to the back of the d-300 right in the middle.

It hasn't been wheeled hard so I don't know if it will work well or not.

I know that you must consider how ridged everything is, since I had issues with the bronco.

pics of the xj mount at about post #37
http://rme4x4.com/showthread.php?t=83436&highlight=tanja+nathan&page=3

and more here;
https://picasaweb.google.com/thenag/TransferCaseNp231Dana300

nathan

 

[greenjeep]

Great idea Nathan, I had wondered how people attached a mount to the rear of a t-case. Thanks!!

 

[N-Smooth]

I am using the stock engine and transmission mounts...

It hasn't been wheeled hard so I don't know if it will work well or not.

it won't work well or rather for long. xj's chew up stock motor mounts in stock form. wheeling the crap out of them is like throwing gas on a fire. spend the money on some new mounts and you'll be happy. the proof is in the pudding that MORE makes good mounts, just ask herzog. some people that race their xj's (the crazies ) have problems with the block side of the mounts breaking, hence brown dog offering a super-beef solution. back in the day i had a bad spell of death wobble that finished off my pass side motor mount and pushed my oil filter into a sharp point on the inside of the frame rail... it was a mess.

greenjeep- you have been steered in the right direction with just using bushings similar to the ones you have for motor mounts. if they break up and fail your drivetrain will only have an inch or so to fall and that will be it since the bolt will still be stuck in the bushing housing. hopefully that will prevent the puncturing of your trans pan but honestly i can't imagine them failing anyways